The invention relates generally to the field of imaging systems. In particular, the invention relates to the detection of X-rays in an X-ray imaging device.
Non-invasive imaging broadly encompasses techniques for generating images of the internal structures or regions of a person or object that are otherwise inaccessible for visual inspection. For example, non-invasive imaging techniques are commonly used in the industrial field for inspecting the internal structures of parts and in the security field for inspecting the contents of packages, clothing, and so forth. One of the best known uses of non-invasive imaging, however, is in the medical arts where these techniques are used to generate images of organs and/or bones inside a patient which would otherwise not be visible.
One class of non-invasive imaging techniques that may be used in these various fields is based on the differential transmission of X-rays through a patient or object. In the medical context, a simple X-ray imaging technique may involve generating X-rays using an X-ray tube or other source and directing the X-rays through an imaging volume in which the part of the patient to be imaged is located. As the X-rays pass through the patient, the X-rays are attenuated based on the composition of the tissue they pass through. The attenuated X-rays then impact a detector that converts the X-rays into signals that can be processed to generate an image of the part of the patient through which the X-rays passed based on the attenuation of the X-rays. Typically the X-ray detection process utilizes a scintillator, which generates optical photons when impacted by X-rays, and an array of photosensitive elements, which generate electrical signals based on the number of optical photons detected.
Some X-ray techniques utilize very low energy X-rays so that patient exposure can be extended. For example, fluoroscopic techniques are commonly used to monitor an ongoing procedure or condition, such as the insertion of a catheter or probe into the circulatory system of a patient. Such fluoroscopic techniques typically obtain large numbers of low energy images that can be consecutively displayed to show motion in the imaged area in real-time or near real-time.
However fluoroscopic techniques, as well as other low energy imaging techniques, may suffer from poor image quality due to the relatively weak X-ray signal relative to the electronic noise attributable to the detector. As a result it is typically desirable to improve the efficiency of the detection process, such as by generating more signal at the detector for each absorbed X-ray. One factor that reduces the efficiency of the detection process is the number of optical photons absorbed or reflected between the scintillator and the photosensitive elements.
In particular, an electrode is typically situated between the scintillator and the photosensitive elements. While the electrode allows a photodiode of each photosensitive element to function properly, and thus allows the optical photons to be detected, the electrode also lies over most of the photosensitive element. Since the electrode is typically constructed of a metal, such as indium-tin-oxide (ITO) and is not completely transparent to optical light some of the optical photons generated by the scintillator are absorbed or reflected by the electrode. As a result, optical photons that might otherwise be detected, and thereby provide additional signal, never reach the photosensitive elements.
Therefore there is a need for a suitable electrode that addresses some or all of the problems set forth above.